Utilizing techniques developed in our laboratory the blood flows to normal and malignant tissues during hyperthermic treatment will be estimated with microspheres 25u in diameter. To perform these studies the nonmetastasizing MTW-9B and metastasizing SMT-2A mammary adenocarcinomas will be transplanted into the inguinal mammary glands of the female isogeneic W/Fu rats. The tissues will be heated with dielectric loaded (titania) contact applicators tuned to operate at either 180 or 1,000 MHz. The applicators will be connected to a variable frequency microwave generator which produces 100 millisecond pulses every 101 milliseconds. The tissue temperature will be automatically maintained within plus or minus .1 C by an electronic control circuit which compares a preset temperature to that registered by a tissue implanted thermistor probe during the 1 millisecond off period. Our previous studies demonstrated that at 180 MHz malignant tissue absorbs a significantly greater amount of power than normal tissues. Tumor growth/regrowth studies will be performed to determine whether microwave heating at 180 MHz is more cytotoxic than treating at 1000 MHz. Similar tumor growth/regrowth experiments will be performed to determine whether the infusion of vasoactive drugs and/or sodium bicarbonate improves the hyperthermic treatment of tumors.